In most joint arthroplasty, replacement and/or reconstruction surgery procedures, and in particular in hip and shoulder joint surgery, a joint is replaced by a prosthetic implant. The main goal of such interventions is to relieve (arthritic) pain and/or to restore severe physical joint damage. When prosthesis fails, a revision surgery is carried out. However, this procedure is technically more difficult and time-consuming than the primary intervention and the outcome is often less satisfactory, both because there is less bone stock to work with and because the removal of adherent cement or prosthetic components may result in fracture or perforation of the bone. Furthermore, with each successive joint revision, the risk of infection and symptomatic loosening of the prosthesis may increase substantially. Accordingly, one of the most important aspects of joint surgery procedures is the correct, accurate and stable placement of the primary implant.
Correct implant placement is important in shoulder surgery, and particularly important in hip surgery. The majority of acetabular implants used in hip surgery are currently placed using the press-fit technique. In this technique, the patient's acetabulum is first reamed with a sequence of hemispherical reamers with increasing diameters, such that a hemispherical cavity is created at the location where the implant should be placed. The final (largest) reamer typically has a diameter smaller than that of the implant. In a further step, the implant is attached to an impactor and placed upon the pelvis of the patient, such that the implant supports on the rim of the reamed cavity and the orientation of the implant is anatomically suitable. Finally, the impactor is hit with a hammer until the implant sits inside the reamed cavity. Thereafter, the implant is released from the impactor.
The general consensus in the field is that the orientation of the implant determines the success of the surgery and the lifespan of the implant (Hayakawa et al., Archives of orthopedic and trauma surgery Vol. 129 (2009):1151-1156). However, the current procedure shows several shortcomings for obtaining a good orientation. Indeed, the only anatomical visual reference during final placement is the orientation of the transverse ligament (Pearse et al., Hip international Vol. 18 (2008):7-10), to which the top plane of the implant should be oriented in parallel. Accordingly, rotation around the axis of the transverse ligament remains a variable parameter. In addition, the transverse ligament is generally obscured from the surgeon's view, further hampering the orientation process. Furthermore, the impactor and hammer are both rather bulky, making it difficult to keep the impactor in a stable orientation.
Few practical solutions have been proposed for these problems. US patent application 2009/0163922 (Meridew, Metzger) describes a patient-specific guide to be positioned and optionally attached to the acetabular rim, designed to interface with the impactor so as to enforce the correct orientation. However, it is very doubtful whether such a device could be able to withstand the momentum applied to it during impaction.
Accordingly, there is a need for alternative and improved surgical devices, and in particular surgical guiding instruments, which provide the ability to correctly and accurately insert, place and orient an implant into a patient's joint.